It is known for such a drive mechanism to include an electric motor unit that has a stationary end and a rotating end. The rotating end being arranged for rotating a winding core for receiving wound layers of a flexible element. It has further been proposed for such a drive mechanism to also include a spring assist module for compensating the masses of the architectural covering between its opposite first and second end positions.
In a known architectural covering, as disclosed in applicant's international patent application published as WO 2010/089118, the spring assist module is required to be positioned at an outer end of the roller tube because its stationary central shaft requires a fixed connection to one of the mounting brackets. As a consequence the motor unit is arranged at an inward end of the spring assist module and is difficult to reach for adjustment or control. It would for instance be desirable when adjusting the end position limits, that it would not be necessary to disassemble the spring assist and motor units from the roller blind to enable such adjustments.